1. Field of the Invention
The present invention relates to an organic electroluminescent device (hereinafter, referred to as an “OLED”). More particularly, the present invention relates to a flexible organic electroluminescent device for blocking moisture from being infiltrated into the organic electroluminescent device to enhance the life of the organic electroluminescent device, and a method for fabricating the same.
2. Discussion of the Related Art
An organic electroluminescent device, which is one type of flat panel display (FPDs), may have high brightness and low operation voltage characteristics. Furthermore, the organic electroluminescent device has a high contrast ratio because of being operated as a self-luminous type display that spontaneously emits light, and allows the implementation of an ultra-thin display. Furthermore, the organic light-emitting diode has advantages such as facilitating the implementation of moving images using a response time of several microseconds (μs), having no limitation in viewing angle, having stability even at low temperatures, and being driven at low voltages between DC 5 to 15 V, thus facilitating the fabrication and design of a driving circuit thereof.
Furthermore, the fabrication process of the organic electroluminescent device can be carried out using only deposition and encapsulation equipment, and therefore the fabrication process is very simple.
The organic light-emitting diode having such characteristics can be largely divided into a passive matrix type and an active matrix type. In the passive matrix type, a device may be configured with a matrix form in which the scan and signal lines are crossed with each other, and the scan lines are sequentially driven as time passes to drive each pixel. Thus, instantaneous brightness as much as average brightness multiplied by the number of lines may be required to display the average brightness.
The active matrix type has a structure in which thin-film transistors, which are switching devices for turning on or off a pixel region, are located in each pixel region, and drive transistors connected to the switching transistors are connected to a power line and organic light emitting diodes, and formed in each pixel region.
Here, a first electrode connected to the drive transistor may be turned on or off in the pixel region unit, and a second electrode facing the first electrode may perform the role of a common electrode, thereby implementing an organic light emitting diode along with an organic light emitting layer interposed between the two electrodes.
In the active matrix type having such characteristics, a voltage applied to the pixel region may be charged at a storage capacitance (Cst), and applied until the next frame signal is applied and thus continuously driven for one screen regardless of the number of scan lines.
Accordingly, the same brightness can be obtained even if a low current is applied, thereby having an advantage of providing low power consumption, fine pitch and large screen sized display, and thus in recent years, active matrix type organic electroluminescent devices have been widely used.
The fundamental structure and operating characteristics of such an active matrix type organic electroluminescent device will be described below with reference to the accompanying drawings.
FIG. 1 is a circuit diagram for one pixel region in a typical active matrix type organic electroluminescent device.
Referring to FIG. 1, one pixel region of a typical active matrix type organic electroluminescent device 10 may include a switching thin film transistor (STr), a drive thin film transistor (DTr), a storage capacitor (Cst), and an organic light emitting diode (E).
A gate line (GL) is formed in the first direction, and a data line (DL) disposed in the second direction crossed with the first direction to define a pixel region (P) along with the gate line (GL) is formed, and a power line (PL) separated from the data line (DL) to apply a power voltage is formed.
Furthermore, a switching thin film transistor (STr) is formed at a portion where the data line (DL) and gate line (GL) are crossed with each other, and a drive thin film transistor (DTr) electrically connected to the switching thin film transistor (STr) is formed within the each pixel region (P).
Here, the drive thin film transistor (DTr) is electrically connected to the organic light emitting diode (E). In other words, a first electrode, which is one side terminal of the organic light emitting diode (E), is connected to a drain electrode of the drive thin film transistor (DTr), and a second electrode, which is the other terminal thereof, is connected to the power line (PL). Here, the power line (PL) transfers a power voltage to the organic light emitting diode (E). Furthermore, a storage capacitor (Cst) is formed between a gate electrode and a source electrode of the drive thin film transistor (DTr).
Accordingly, when a signal is applied through the gate line (GL), the switching thin film transistor (STr) is turned on, and the signal of the data line (DL) is transferred to the gate electrode of the drive thin film transistor (DTr) to turn on the drive thin film transistor (DTr), thereby emitting light through the organic light emitting diode (E). Here, when the drive thin film transistor (DTr) is in a turned-on state, the level of a current flowing through the organic light emitting diode (E) from the power line (PL) is determined, and due to this, the organic light emitting diode (E) may implement a gray scale, and the storage capacitor (Cst) may perform the role of constantly maintaining the gate voltage of the drive thin film transistor (DTr) when the switching thin film transistor (STr) is turned off, thereby allowing the level of a current flowing through the organic light emitting diode (E) to be constantly maintained up to the next frame even when the switching thin film transistor (STr) is in an off state.
FIG. 2 is a plan view schematically illustrating an organic electroluminescent device according to the related art.
FIG. 3 is a schematic cross-sectional view of an organic electroluminescent device along line III-III in FIG. 2 according to the related art.
Referring to FIG. 2, according to an organic electroluminescent device 10 according to the related art, a display area (AA) is defined on a substrate 11, and a non-display area (NA) is defined at the outside of the display area (AA), and a plurality of pixel regions (P), each defined as a region surrounded by the gate line (not shown) and the data line (not shown) are provided, and the power line (not shown) is provided in parallel to the data line (not shown) in the display area (AA).
Here, a switching thin film transistor (ST) (not shown) and a drive thin film transistor (DTr) (not shown) are formed in the plurality of pixel regions (SP), respectively, and connected to the drive thin film transistor (DTr).
According to an organic electroluminescent device 10 according to the related art, the substrate 11 formed with the drive thin film transistor (DTr) and organic light emitting diode (E) is encapsulated by a passivation layer (not shown).
Specifically describing the organic electroluminescent device 10 according to the related art, as illustrated in FIG. 3, the display area (AA) is defined, and the non-display area (NA) is defined at the outside of the display area (AA) on the substrate 11, and a plurality of pixel regions (P), each defined as a region surrounded by the gate line (not shown) and the data line (not shown) are provided, and the power line (not shown) is provided in parallel to the data line (not shown) in the display area (AA).
Here, an insulation material, for example, a buffer layer (not shown) formed of silicon oxide (SiO2) or silicon nitride (NiNx), which is an inorganic insulation material, is provided on the substrate 11.
Furthermore, a semiconductor layer 13 made of pure polysilicon to correspond to the drive region (not shown) and switching region (not shown), respectively, and comprised of a first region 13a forming a channel at the central portion thereof and second regions 13b, 13c in which a high concentration of impurities are doped at both lateral surfaces of the first region 13a is formed at each pixel region (P) within the display area (AA) at an upper portion of the buffer layer (not shown).
A gate insulating layer 15 is formed on the buffer layer (not shown) including the semiconductor layer 13, and the drive region (not shown) and switching region (not shown) are provided on the gate insulating layer 15, and thus a gate electrode 17 is formed to correspond to the first region 13a of each of the semiconductor layer 13.
Furthermore, a gate line (not shown) connected to a gate electrode 17 formed in the switching region (not shown) and extended in one direction is formed on the gate insulating layer 15.
On the other hand, an interlayer insulating layer 19 is formed on an entire surface of the display area at an upper portion of the gate electrode 17 and gate line (not shown). Here, a semiconductor layer contact hole (not shown) for exposing the second regions 13b, 13c, respectively, located at both lateral surfaces of the first region 13a of each of the semiconductor layer, is provided on the interlayer insulating layer 19 and the gate insulating layer 15 at a lower portion thereof.
Furthermore, a data line (not shown) crossed with a gate line (not shown) to define the pixel region (P) and formed of a second metal material, and a power line (not shown) separated therefrom are formed at an upper portion of the interlayer insulating layer 19 including the semiconductor layer contact hole (not shown). Here, the power line (not shown) may be formed to be separated from and in parallel to the gate line (not shown) on a layer formed with the gate line (not shown), namely, the gate insulating layer.
In addition, a source electrode 23a and a drain electrode 23b brought into contact with the second regions 13b, 13c separated from each other, and respectively exposed through the semiconductor layer contact hole (not shown) and formed of the same second metal material as that of the data line (not shown) are formed in the each drive region (not shown) and switching region (not shown) on the interlayer insulating layer 19. Here, the semiconductor layer 13 and gate insulating layer 15 sequentially deposited on the drive region (not shown) and the gate electrode 17 and interlayer insulating layer 19 and the source electrode 23a and drain electrode 23b formed to be separated from each other forms a drive thin film transistor (DTr).
On the other hand, an organic insulating layer 25 having a drain contact hole (not shown) for exposing the drain electrode 23b of the drive thin film transistor (DTr) is formed on the drive thin film transistor (DTr) and switching thin film transistor (not shown).
Furthermore, a first electrode 31 brought into contact with the drain contact hole (not shown) through the drain electrode 23b and the drain contact hole (not shown) of the drive thin film transistor (DTr) and having a separated form for each pixel region (P) is formed on the organic insulating layer 25.
In addition, a bank 33 formed to divide each pixel region (P) is formed on the first electrode 31. Here, the bank 33 is disposed between adjoining pixel regions (Ps). Furthermore, the bank 33 is not only formed between adjoining pixel regions (Ps), but also part thereof 33a is formed in a panel edge portion, namely, non-display area (NA).
An organic light emitting layer 35 comprised of organic light emitting patterns (not shown) for emitting red, green and blue colors, respectively, is formed on the first electrode 31 within each of the pixel regions (Ps) surrounded by the bank 33.
Furthermore, a second electrode 37 is formed on an entire surface of the display area (AA) at an upper portion of the organic light emitting layer 35 and bank 33. Here, the first electrode 31 and second electrode 37 and the organic light emitting layer 35 interposed between the two electrodes 31, 37 form an organic light emitting diode (E).
On the other hand, a first passivation layer 39 is formed on an entire surface of the substrate including the second electrode 37 as an insulating layer for preventing moisture permeation.
Furthermore, an organic layer 41 made of a high organic molecular substance such as a polymer is formed in the display area (AA) on the first passivation layer 39.
In addition, a second passivation layer 43 made of an insulation material, for example, silicon oxide (SiO2) or silicon nitride (SiNx) which is an inorganic insulation material, is additionally formed on the first passivation layer 39 including the organic layer 41 to block moisture from being infiltrated through the organic layer 41.
Moreover, a barrier film 47 for the encapsulation of the organic light emitting diode (E) and the prevention of upper moisture permeation is located on an entire surface of the substrate including the second passivation layer 43 to face the substrate, and a press sensitive adhesive (hereinafter, referred to as a “PSA”) 45 is completely attached to and interposed between the substrate 11 and barrier film 47 with no air layer. Here, the second passivation layer 43, the press sensitive adhesive 45, and the barrier film 47 form a face seal structure.
In this manner, the substrate 11 is fixed to the barrier film 47 through the adhesive 45 to form a panel, thereby configuring the organic electroluminescent device 10 according to the related art.
However, according to an organic electroluminescent device 10 in accordance with the related art, the second passivation layer 43 and barrier film 47 perform the role of a barrier for preventing moisture permeation in the existing face seal structure, for example, in a layer structure with the second passivation layer 43, press sensitive adhesive 45 and barrier film 47, but the press sensitive adhesive 45 performs the role of a barrier in a relatively inefficient manner. As a material issue, the probability of moisture permeation at the lateral surface is higher than that at the upper portion.
When foreign substances or cracks are not generated between each thin films in the face seal structure, moisture permeation does not occur in an abnormal manner, but moisture permeation occurs due to foreign substances or the like that are generated during the process.
In particular, bad step coverage on the first and the second passivation layer 43 forms a boundary surface around foreign substances, which is used as a moisture infiltration path.
Accordingly, moisture (H2O) infiltrated through the press sensitive adhesive 45 having a low barrier capability performs first moisture permeation through the boundary portion of foreign substances, and second moisture permeation is diffused through a lower organic layer of the thin-film transistor, for example, a bank, an interlayer insulating layer (i.e., planarization layer), and the like, thereby oxidizing a cathode electrode of the organic electroluminescent device.
FIG. 4 is an enlarged cross-sectional view schematically illustrating that moisture (H2O) infiltrated through a crack generated when cutting a scribe line of the organic electroluminescent device is propagated through the first and the second passivation layer, as an enlarged cross-sectional view of portion “A” in FIG. 3.
FIG. 5 is a view schematically illustrating a phenomenon in which a crack is propagated through the first and the second passivation layer when cutting a scribe line of the organic electroluminescent device according to the related art using a cutting wheel.
As illustrated in FIGS. 4 and 5, when the scribe line 50 of the organic electroluminescent device is cut using a cutting wheel 60, glass damage due to the wheel scribe may generate a crack by an external shock while being processed or moved during the inspection process or the like, which becomes a path of moisture permeation at the lateral surface while being propagated through the first and the second passivation layer 39, 43.
Furthermore, moisture may be propagated through an organic layer during the generation of a crack of the first and the second passivation layer 39, 43 exposed at an outer portion of the press sensitive adhesive 45 or barrier film 47.
Accordingly, moisture may be infiltrated due to a crack of the first and the second passivation layer 39, 43 initiated from the scribe line 50 in such a manner to form a non-light-emitting region in the display area portion (AA).
In addition, a crack of the first and the second passivation layer 39, 43 may be generated from a panel edge portion due to an external shock or the like and propagated to the light emitting portion, thereby forming a non-light-emitting region in the display area portion (AA).